Integral turning gear for turbine rotors

ABSTRACT

An integral turning gear is machined onto one-half of a turbine rotor shaft coupling or on a pedestal of a rotor shaft for engagement with a motorized pinion for rotating the shaft of the turbine, for example during shutdown. The gear teeth are integrally formed on the coupling or shaft and do not require additional length of axial rotor span or introduce significant stresses. The motorized pinion may engage the integral turning gear teeth to rotate the rotor, for example, during turbine shutdown to prevent the rotor from sagging while cooling from elevated temperatures.

The present invention relates to a turning gear for turbine rotors and particularly relates to an integral turning gear formed on at least one of the coupling flanges joining rotor sections to one another or on a pedestal on the rotor enabling a motor pinion in engagement with the integral turning gear to turn the rotor.

BACKGROUND OF THE INVENTION

In many different types of turbines, it is desirable to rotate the rotor by an ancillary motor driven pinion. For example, during start-up and shut down of a steam turbine and while the turbine remains at elevated temperatures for an extended period of time, the rotor is typically turned at a slow rate for example on the order to 2 or 3 rpm. Otherwise, the rotor may tend to sag if it remains stationary at elevated temperatures during shutdown. The motor pinion is, of course, disconnected from the turbine rotor shaft during normal turbine operations.

Two types of turning gears have been traditionally used, for example on steam turbines, to rotate the rotor. A spacer disk gear has been interposed between the end coupling of rotor shaft sections. The spacer disk gear includes a through bored steel disk with gear teeth machined about its outer diameter for interfacing with the pinion of the turning motor. The disk has a bolt hole pattern matching the bolt hole pattern of the rotor shaft sections. The disk is secured by bolting it between the two coupling halves, e.g. typically flanges formed on the ends of the rotor shaft sections. This implementation, however, requires a significant increase in the axial extent of the rotor. Thus space constraints become an issue when using this type of turning gear.

A second traditional type of turning gear is a shrunk-on ring gear. This gear comprises a steel ring with gear teeth machined about its outer diameter and which gear teeth interface with the pinion of the turning motor. To assemble the shrunk-on ring gear, the ring is heated to enable the ring to be slipped onto the rotor coupling or a separate rotor pedestal. When the ring gear cools, the shrinking of the metal holds the ring gear in place on the coupling or pedestal. While this type of turning gear does not require significant axial span, the shrink-induced stresses combined with centrifugal stresses during turbine operation can result in an unacceptable design. Accordingly, there has developed a need for a turning gear for the rotor of a turbine which does not require additional axial span or manifest unacceptable stress levels.

BRIEF DESCRIPTION OF THE INVENTION

In a preferred embodiment of the present invention, there is provided a coupling for a turbine rotor comprising: turbine rotor shaft sections axially aligned with one another and having registering end portions, each shaft section including an integral radial flange having a bolt circle including bolt openings about the registering end portions; bolts through the registering bolt openings of the rotor shaft sections to secure the shaft sections to one another; and gear teeth integral with one of said flanges for engagement by a pinion enabling the rotor for rotation upon meshing engagement of the pinion and the gear teeth with one another.

In a further preferred embodiment of the present invention, there is provided a steam turbine comprising: a turbine rotor shaft forming part of a low pressure section of the steam turbine; said rotor shaft including turbine rotor shaft sections axially aligned with one another and having registering end portions; each shaft section including an integral radial flange having a bolt circle with bolt openings about the registering end portions; bolts through registering bolt openings of the rotor shaft sections to secure the shaft sections to one another; gear teeth integral with and about one of said flanges; and a turning gear in engagement with the gear teeth on the one flange for turning the rotor.

In a still further preferred embodiment of the present invention, there is provided a steam turbine comprising: a turbine rotor shaft forming part of a steam turbine; said rotor shaft having a radially outwardly projecting flange formed integrally with the shaft; gear teeth integral with and about an outer diameter of said radially outwardly projecting flange; and a motorized pinion gear in engagement with said gear teeth on said flange for turning the rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a low pressure section of a steam turbine and illustrating a turning gear formed on a rotor shaft section between the low pressure section and a generator, not shown, in accordance with the prior art, the turning gear being illustrated driving a spacer disk gear;

FIG. 2 is a fragmentary schematic illustration with portions in cross section of the spacer disk gear used to join rotor sections to one another in accordance with a conventional design;

FIG. 3 is a view similar to FIG. 2 illustrating a shrunk-on ring gear forming part of a turning gear of a conventional design; and

FIG. 4 is an enlarged schematic illustration of the integral turning gear of FIG. 1 according to a preferred aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings particularly to FIG. 1, there is illustrated a low pressure section, generally designated 10 for a steam turbine. The low pressure section 10 includes an inlet 11 for flowing steam radially inwardly as indicated by the arrows 12. The steam flow splits for flow in opposite axial directions through steam turbine blading 14 to drive a rotor indicated schematically by the dot dash line 16 in FIG. 1. The rotor 16 at the end of the low pressure turbine 10 is illustrated enlarged and includes a rotor section 18 joined to another rotor section 20 forming part of a generator. The operation of the steam turbine is conventional and further description is not believed necessary. Suffice to say that it is conventional to provide a pinion 22 driven by a motor 23 for rotating the shaft 16 of the turbine by selective engagement of the pinion 22 with a turning gear e.g. carried by a spacer disk gear carried by the shaft 16.

Traditionally as illustrated in FIGS. 2 and 3, two types of gears have been previously used to turn the rotor of the turbine, for example during turbine start-up and shutdown. One type of gear illustrated in FIG. 2 is a spacer disk 24 with gear teeth 26 machined onto the outer diameter surface. The gear teeth 26 are provided for meshing engagement with the motor pinion 22. As illustrated in FIG. 2, the disk 24 has a bolt hole pattern 28 which matches a bolt hole pattern 30 through the end shaft coupling, e.g. flanges 32 and 34 of the rotor shaft sections 18 and 20 respectively. Thus, bolts 36 pass through the flanges 32, 34 and the disk gear 24. It will be appreciated from a review of FIG. 2 that the disk gear 24 necessarily requires an axial extension of the overall length of the turbine shaft which can be an issue where space is a design constraint.

In FIG. 3, there is illustrated a second type of gear conventionally used to facilitate meshing engagement with the motor pinion 22. In FIG. 3, there is illustrated a shrunk-on ring gear 40 which consists of a steel ring 42 with gear teeth 44 machined about its outer surface. Gear teeth 44 are for meshing engagement with the gear teeth of the motor pinion 22. To assemble the shrunk-on ring gear 40 onto the flange or a pedestal on the rotor shaft, the ring is heated to allow it to be slipped onto the rotor coupling or pedestal. When it cools, the metal shrinks and holds the ring gear in place. This type of interface with a motor pinion is useful where axial space constraints are an issue. However, the shrink-induced stresses combine with the centrifugal stresses can result in an unacceptable design.

Referring now to FIGS. 1 and 4, there is illustrated an integral turning gear mounted on the rotor shaft in accordance with a preferred aspect of the present invention. Particularly, the rotor shaft includes rotor shaft sections 50 and 52 having a coupling including integral radial flanges 54 and 56, respectively. The shaft sections 50 and 52 are axially aligned with one another and having registering abutting end face portions 51 and 53, respectively. As illustrated, flange 56 extends radially outwardly beyond the radial extent of flange 54. Each of the flanges 54 and 56 includes a bolt circle including bolt openings 58 and 60 respectively to receive bolts 62 and 64 whereby the shaft sections can be secured to one another. Gear teeth 66 are provided about the outer diameter of the flange 56 for engagement with the motor pinion 68 whereby the motor driven pinion in engagement with gear teeth 66 turns the rotor sections 50 and 52 and hence the rotor 16 of the turbine.

It will be appreciated that the gear teeth 66 are formed integrally on the turning gear flange 56. Alternatively, the gear teeth 66 may be integrally formed on a radially projecting pedestal on the rotor shaft intermediate rotor ends rather than on a coupling between discrete shaft sections. It will also be appreciated that the gear teeth 66 integral with one-half of the coupling or with the pedestal not only do not require additional axially space but also provide low stress levels since there is no shrink fitting of a toothed gear ring onto the coupling or pedestal. By integral gear teeth or an integral turning gear is meant that there is no separate part carrying gear teeth which is secured to the rotor.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. A coupling for a turbine rotor comprising: turbine rotor shaft sections axially aligned with one another and having registering end portions, each shaft section including an integral radial flange having a bolt circle including bolt openings about the registering end portions; bolts through said registering bolt opening of the rotor shaft sections to secure the shaft sections to one another; and gear teeth integral with one of said flanges; for engagement by meshing engagement of a pinion enabling the rotor for rotation upon connecting the pinion and the gear teeth.
 2. A rotor according to claim 1 wherein said end portions include end faces of said shaft sections in abutting relation with one another.
 3. A steam turbine comprising: a turbine rotor shaft forming part of a low pressure section of the steam turbine; said rotor shaft including turbine rotor shaft sections axially aligned with one another and having registering end portions; each shaft section including an integral radial flange having a bolt circle with bolt openings about the registering end portions; bolts through registering bolt openings of the rotor shaft sections to secure the shaft sections to one another; gear teeth integral with and about one of said flanges; and a pinion gear in engagement with the gear teeth on the one flange for turning the rotor.
 4. A turbine according to claim 3 wherein said end portions include end faces of said shaft sections in axial abutting relation to one another.
 5. A steam turbine comprising: a turbine rotor shaft forming part of a steam turbine; said rotor shaft having a radially outwardly projecting flange formed integrally with the shaft; gear teeth integral with and about an outer diameter of said radially outwardly projecting flange; and a motorized pinion gear in engagement with said gear teeth on said flange for turning the rotor. 